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Miniature wireless power demonstrator

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Marko

Tue Mar 12 2013, 10:37PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi

From purely theoretical point of view, the only thing that really matters is the Q factor of the resonators; the frequency itself is irrelevant. But, low frequency will result in too big reactive components, and too high frequency will increase losses due to skin effect, as well as make the system radiate more spurious radio waves.

Looking at your amplifier, to me it looks like a radio transmitter amp designed to drive a 50 ohm resistive load at a certain frequency. Both impedance and resonant frequencies will change if you alter the coupling between resonators or change the load, so a setup like this is best suited for static demonstrations with fixed resonator distance and a light bulb as a load.

While RF amplifier will probably tolerate some reflected power, it can't be guaranteed not to blow up if it has no protection circuits installed.

When resonators are weakly coupled, both modes of the system will be very near the free resonant frequencies of each resonator alone, so you'd probably want to tune up for that.

The feeder loop that is coupled to the transmitting resonator forms an air cored transformer that performs impedance matching to the amplifier. Inverse is done on the receiver side in order to match into the light or whatever other load. A right way to design it would be to simulate the whole system in a FEMM software and wind the exact required coupling and number of turns for your feeder coil/loop.Note that this kind of coupling will always present some inductive reactance to the amplifier due to low magnetizing inductance of the loop, adding to amplifier unhappiness.

I think Steve Conner had some success with a setup like this, where he used his HAM amplifier to drive the power into system. I'm not sure how much can I help without knowing more details about the amplifier!

Regarding the cap in my receiver, I just used one because reactive power was lower there than on the transmitter (since it's only weakly coupled most of the time) and it seemed to be enough. If your resonators will be placed at cl0ose distance for high power transfer, you'd probably want identical cap banks in both of them.

Marko

zero_coke

Wed Mar 13 2013, 06:41PM

Registered Member #8368 Joined: Wed Nov 28 2012, 04:11AM
Location:
Posts: 9

Thanks very much Marko!

Yeah I think I just destroyed my power amplifier...it is a radio transmitter power amp so I probably screwed up somewhere but I don't know where...I simply connected it to the load and made sure the impedance of my transmitting coil was 50 ohms by adding a series resistor to top up the impedance of the coil to a total of 50 ohms.

I don't think it has to do with reflected power because I'm not at high enough frequencies for such phenomena of reflections to occur right? I'm at 2 MHz so lambda = 150 m and lambda / 40 = 3.75m (general rule for circuit size vs reflections, correct me if I'm wrong) and my circuit is definitely smaller than 3.75m so I don't think I have to worry about microwave phenomena here...or do I ?

I contacted Steve Conner to see how he used the ham radio amplifier in this setup. I thought it'd be straightforward but I guess not...

electronics-PCB

Thu Mar 28 2013, 06:32PM

Registered Member #11011 Joined: Tue Mar 12 2013, 09:03AM
Location: Helsinki, Finland, Europe.
Posts: 1

Hello everybody!
First of all: thank you Marko for sharing this work and for starting this thread.
I did a small demo and videod it at my job/firm. I tried to decent and thank Marko and you all at the end of the video...
If interested you can find the video here:

Basic lightbulb demo, but I experimented with ferromagnetic toroids at the final part of the video.
This would be fun to continue, because I simulated versions of the project with over a 40% efficiency....lets see if I can get the funds + time for this sometime.

Cheers, esa

Ynicky

Sat Apr 20 2013, 09:46AM

Registered Member #12317 Joined: Thu Mar 28 2013, 07:04PM
Location:
Posts: 2

Hi all!
This is my version of Marko's project.

Veronica P.

Mon May 20 2013, 01:48AM

Registered Member #16001 Joined: Fri May 03 2013, 10:31AM
Location:
Posts: 3

Hi there,
I'm trying to recreate Marko's circuit, but it doesn't work. I also used different inductors. I used 100u, then 150u and 200. There was a LOT of smoking and popping. Can anyone explain why that happened?

Ynicky

Tue May 21 2013, 03:36PM

Registered Member #12317 Joined: Thu Mar 28 2013, 07:04PM
Location:
Posts: 2

To Veronica:
What has burned? Inductors, MOSFETs or relay?
What type of MOSFETs?
Have D1, D2 right connection?
What capacitance have C1...C8?

Veronica P.

Sun May 26 2013, 07:02AM

Registered Member #16001 Joined: Fri May 03 2013, 10:31AM
Location:
Posts: 3

Ynicky,
I've managed to fix the problem,
The inductors had burned. The MOSFETS are the ones Marko outlined- IRFZ44N, the capacitors were also all 6.8uF, with one being 100nF.
The problem was I was substituting one 47uF capacitor for the smaller ones, and one of my resistors was not the correct value.

Veronica P.

Sat Jun 01 2013, 05:12AM

Registered Member #16001 Joined: Fri May 03 2013, 10:31AM
Location:
Posts: 3

Hi,
Has anyone done a circuit analysis of their wireless power transfer circuits? Which equations are the best to focus on?
(I mean to look at the characteristics of the circuit)

jechwa

Fri Aug 30 2013, 02:31PM

Registered Member #33559 Joined: Wed Aug 28 2013, 01:43PM
Location:
Posts: 5

Hi,
I build Markos transmitter and did some experiments. I found that it is possible to increase the transfer distance using passive LC tank circuits.
At the moment I reach a distance seven times the coil diameter of the Rx coil: 70cm.
See my youtube video:

http://www.youtube.com/channel/UCP6EEu4DG22gg-6l0L4ATJA

cheers
Jens

jechwa

Fri Aug 30 2013, 02:42PM

Registered Member #33559 Joined: Wed Aug 28 2013, 01:43PM
Location:
Posts: 5

Veronica P. wrote ...

Ynicky,
I've managed to fix the problem,
The inductors had burned. The MOSFETS are the ones Marko outlined- IRFZ44N, the capacitors were also all 6.8uF, with one being 100nF.
The problem was I was substituting one 47uF capacitor for the smaller ones, and one of my resistors was not the correct value.

6.8 ÂµF, 47ÂµF are to high! You mean nF ?

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